This invention relates to an optical module and a connecting construction for an optical module which are used mainly in an optical communication equipment or the like.
Conventional optical modules can be roughly classified into those of pigtail type in which a module main body is provided with a pigtail cord which is connected with an external optical fiber cord by a connector, and those of receptacle type in which an external optical fiber cord is directly connected with an adapter of a module main body.
In the optical modules of pigtail type, an optical fiber having a covering portion is present in the module and this covering portion not resistant to heat may be deteriorated. Accordingly, it is difficult to mount the optical module together with other parts on an electric circuit board in one step by reflow soldering. For this reason, the following manufacturing operations have been conventionally carried out. Heat-resistant parts are mounted on an electric circuit board by reflow soldering. Thereafter, an optical module is manually assembled over the electric circuit board. Such assembling operation is very cumbersome if a multitude of optical modules are necessary.
Further, with optical modules of receptacle type, it is difficult to arrange external optical fiber cord connected with an optical module in vicinity of a light emitting element, thereby necessitating an optical part such as a lens. This disadvantageously stands as a hindrance to miniaturization.
A connecting construction for an optical module as shown in FIG. 8 is known as a construction to avoid the above problems. An optical module J1 is constructed such that an optical element (semiconductor laser diode) 63 and a short optical fiber 64 having one end optically coupled to the optical element 63 are arranged on a substrate 62 accommodated in a package 61 and a sleeve 65 accommodating an unillustrated ferrule mounted on an other end of the short optical fiber 64 is arranged at one end of the package 61. The optical module 31 and an optical fiber cord K1 are optically coupled by inserting a ferrule 67 provided at an end of the optical fiber cord K1 into the sleeve 65 of the optical module J1 (see Japanese Patent No. 2654538, for example).
In the above connecting construction, the optical module J1 and the optical fiber cord K1 are constructed separately from each other. Accordingly, if the circuit board with the optical fiber cord K1 detached is caused to go through reflow soldering or the like, and then the optical fiber cord K1 is mounted on an electrical circuit board when the optical module J1 and the optical fiber cord K1 are mounted on the circuit board, the optical fiber cord K1 not resistant to heat can be mounted on the circuit board without being exposed to a reflow furnace.
On the other hand, a card type optical data link J2 as shown in FIG. 9 has been proposed to reduce the height of a PC card slot of a personal computer (see Japanese Unexamined Patent Publication No. 7-225327, for example). This link J2 is such that an optical module is mounted in a part of the PC card. A connector portion 71 of the optical data link J2 is connected with a connector portion 72 of a plug K2 accommodating optical fibers. The height of the connecting construction tries to be reduced by adopting such a construction.
However, the above optical module J1 has an optical connector construction by the ferrule accommodating the short fiber and the sleeve. There is a limit in miniaturizing the ferrule and the sleeve in order to ensure high precision and strength. Specifically, the thickness of the module cannot be reduced smaller than the diameter of a usually used ferrule, i.e., about 1.25 mm.
Further, even if miniaturization of the ferrules could be realized, the ferrules having a small diameter need to be abutted against each other. At this time, the very thin ferrules need to be inserted into a very small area without damaging the end faces thereof. Accordingly, it is extremely difficult to couple the optical fiber cords. For example, it should be done by using a special jig.
There is also needed a biasing construction for pushing the ferrules against each other by a force of about 9.8 N in order to ensure a sufficient optical coupling. This requires a spare space on the circuit board. Particularly, a coil spring of about 5 mm is provided to produce a biasing force in order to establish a connection, which is called “physical contact”. The provision of a spring makes a space having a dimension of about 10 to 20 mm along the axial direction of the fiber inevitable, which hinders miniaturization.
Since dirt or the like may attach to an end of an optical fiber during, reflowing, a superfluous member such as a protection cover is required, causing a cumbersome handling and an unnecessary cost.
In the connecting construction shown in FIG. 9 as well, the thickness of the connector portion is restricted, which hinders reduction in the height of the optical data link.
While the PC card is accommodated inside a main body of a laptop computer, a semiconductor laser which produces a large amount of heat is formed in a main body of the PC card. Accordingly, heat is produced inside the main body of the laptop computer. Further, a large amount of heat produced by other electric modules inside the main body of the laptop computer may adversely affect the semiconductor laser or like optical element which is not resistant to thermal change.